Shock focusing explosive initiator



June 28, 1966 E. E. MALLORY 3,257,947

SHOCK FOCUSING EXPLOSIVE INITIATOR Filed Dec. 17, 1964 Fig.

' INVENTOR Ernes/ E. Mal/ary BY W ATTORNEY in the prior art.

United States Patent 3,257,947 SHOCK FOCUSING EXPLOSIVE INITIATOR Ernest E. Mallory, Sunnyvale, Calif., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Dec. 17, 1964, Ser. No. 419,255

4 Claims. (Cl. 102-28) This invention relates to an electric detonator for explosives. More particularly, the invention relates to an electrically actuated squib of the exploding film type.

Various types of exploding squibs have been described The main problem in the art has been that of accidental actuation of such squibs by induced radio frequency fields or inadvertently applied low sources, for example. One of the common types of exploding detonators is the so-called exploding bridgewire squib in which the explosion is initiated by means of a small round wire called a bridgewire to which is applied a, high value of electrical energy in a very short time, causing the wire itself to explode and thus producing a high pressure shock wave. Inadvertently applied currents are usually not of this kind and are ordinarily dissipated through the bridgewire without any adverse effects. Bridgewires in the squibs are not, however, completely resistant to accidental destruction without causing initiation of the squib. For example, currents may be applied to the bridgewire which are of a value below that necessary to explode the bridgewire but yet sufiicient to heat it to a melting temperature thereby destroying its electrical function. Also, if the bridgewire has been placed adjacent to a heat sensitive explosive, detonation may result. With some explosives, the heat tends to increase the sensitivity of the explosive, and sometimes increases it to the point at which the explosive will detonate under the influence of mechanical shock.

Accordingly, it is an object of the invention to provide an improved electric detonator for explosives which will not be set 01f by stray currents, but will respond positively to a current of the proper intensity, wave shape and time interval.

It is a further object of the invention to provide an improved electrical squib which combines greater resistance to accidental actuation with positive and reliable response.

The objects of the invention are achieved by substituting for the conventional exploding bridgewire an exploding conductive film disposed in a cup-shaped depression in the insulating contact support in proximity to the main charge which depression is shaped to focus the shock produced by the explosion of the film into a small volume of the main charge. The use of a film of large surface area and large cross-sectional area provides conduction path for inadvertently applied currents which is such that high temperatures are not generated and any heat that is generated is dissipated over a broad area. By means of the shock focusing arrangement, an initiating shock of greater energy density is produced, which permits the use of a main charge of decreased sensitivity.

Other objects and advantages will occur to those skilled in the art from a consideration of the following description when read in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a vertical section through a squib according to the invention;

FIGURE 2 is a cross-section through another embodi- Referring now to FIGURE 1, one of the embodiments of the present invention is there shown as consisting of a cup-shaped metallic housing 10 containing an explosive charge 11, and having the upper, open end thereof closed by a plug 12 made of electrically insulating material. Lower surface 13 of plug 12 is machined or otherwise formed to provide a depression 14 which may take various shapes. Depression 14 may be paraboloid or spheroid, or any other shape, as long as it is capable of producing a convergent shock wave. A spheroidal surface, for example, produces a shock convergent on the center of curvature of the surface.

The surfacevof depression 14 is coated, prior to assembly of the device, with a conductive film 16 of any suitable material, such as graphite. In order to provide electrical connection to film 16, conductors 17 and 18 are embedded in plug 12 and cont-act film 16 near its periphery to provide electrical connection thereto.

As will be understood by those skilled in the art, conductors 17 and 18 are intended to be connected to a high voltage pulse generator which is capable of providing electrical energy of high intensity in a pulse of short duration. Commonly, such a pulse generator would provide a pulse of about one-half Joule in about 5 microseconds. When such a pulse is applied to the device of the invention, film 16 undergoes an explosion similar to the explosion of a bridgewire in a conventional squib. Because of the shape of depression 14, however, the shock wave produced by the explosion of film 16 is focused on a small volume of the main charge, as suggested at point 19 within the body of the charge 11. Thus, a mechanical shock of increased energy density is produced, and the sensitivity of charge 11 may be accordingly reduced over that now commonly employed.

In FIGURE 2 an alternative embodiment of the invention is shown in which the contact arrangement has been varied. In this arrangement, the depression 14 is provided as in the embodiment of FIGURE 1, but electrical contact is made thereto by means of a centrally disposed contact, 20, and a peripheral contact 21. Contact 21 is shown in detail in FIGURE 3 as consisting of an annular ring 22, which is shaped at 23 to conform to the shape of depression 14. A terminal connector 24 is provided to connect contact 22. with the power supply.

The embodiment of FIGURE 2 operates in much the same way as the embodiment of FIGURE 1, except that the current-path through the film 16 is different because of a diiferent arrangement of the contacts. In the case of each embodiment, the shock focusing elfect is present -to enable the sensitivity of the main charge to' be reduced. The objects of the invention as set forth above are therefore fulfilled by this device.

Obviously, many modifications and variations of the invention are possible in the light of the above teachings. It is therefore to be understood that Within the scope of the appended claims, the invention may he practiced otherwise than as herein specifically described.

What is claimed is: Y

1. An explosive squib consisting of a container,

a low sensitivity explosive material in said container,

an insulating electrode support in said container in contiguous relation to said explosive, said electrode support having a centrally located cup-shaped depression with a curved bottom surface formed therein,

a conductive film deposited over the surface of said depression, contacting a portion of said low sensitivty' explosive which projects into said depression, an

electrode means coupled to said film for connecting said film to a source of high voltage electrical energy, whereby when said conductive film is exploded by the application thereto of a high voltage, short time pulse of electrical energy, the resulting shock wave will be focused into a limited volume of said low sensitivity explosive to provide an energy density sufiicient to initiate said explosive.

2. An exploding film initiator for low sensitivity explosives as recited in claim 1 wherein said electrode means consists of a pair of conductors, each connected to the peripheral edge of said film.

3. An exploding film initiator for low sensitivity explosives as recited in claim 1, wherein said electrode means consists of one contact connected to said film at its center and another contact comprising a ring connected to the peripheral edge of said film.

4. An exploding film initiator for low sensitivity explosives as recited in claim 3, in which said ring con tact is separate from said container.

References Cited by the Examiner UNITED STATES PATENTS 15 BENJAMIN A. BORCHELT, Primary Examiner. R. V. LOTTMANN, Assistant Examiner. I 

1. AN EXPLOSIVE SQUIB CONSISTING OF A CONTAINER, A LOW SENSITIVITY EXPLOSIVE MATERIAL IN SAID CONTAINER, AN INSULATING ELECTRODE SUPPORT IN SAID CONTAINER IN CONTIGUOUS RELATION TO SAID EXPLOSIVE, SAID ELECTRODE SUPPORT HAVING A CENTRALLY LOCATED CUP-SHAPED DEPRESSION WITH A CURVED BOTTOM SURFACE FORMED THEREIN, A CONDUCTIVE FILM DEPOSITED OVER THE SURFACE OF SAID DEPRESSION, CONTACTING A PORTION OF SAID LOW SENSITIVITY EXPLOSIVE WHICH PROJECTS INTO SAID DEPRESSION, AND ELECTRODE MEANS COUPLED TO SAID FILM FOR CONNECTING SAID FILM TO A SOURCE OF HIGH VOLTATE ELECTRICAL ENERGY, WHEREBY WHEN SAID CONDUCTIVE FILM IS EXPLODED BY THE APPLICATION THERETO OR A HIGH VOLTAGE, SHORT TIME PULSE OF ELECTRICAL ENERGY, THE RESULTING SHOCK WAVE WILL BE FOCUSED INTO A LIMITED VOLUME OF SAID LOW SENSITIVITY EXPLOSIVE TO PROVIDE AN ENERGY DENSITY SUFFICIENT TO INITIATE SAID EXPLOSIVE. 